The present invention relates to a fuel injector.
U.S. Pat. No. 4,803,393 describes a fuel injector known for fuel injection systems in internal combustion engines, which is executed using a piezoelectric actuator. Using the actuator, a valve-closure member, which cooperates with a valve seat surface forming a sealing seat, can be actuated via a valve needle. The actuator can be actuated in a first direction of motion, and the valve-closure member can be moved by the valve needle in a second direction of motion that is essentially perpendicular to the first direction of motion. Between the actuator and the valve needle, a hydraulic transmission device is provided, the actuator being connected, via a first transmission piston, to a transmission chamber of the transmission device, the chamber being filled with a hydraulic fluid and being essentially bent in an L-shape, and the valve needle being connected thereto via a second transmission piston. The known fuel injector can only be used as a so-called inward-opening fuel injector.
German Published Patent Application No. 195 00 706, describes a fuel injector. In the fuel injector described in this publication, a piezoelectric actuator is provided for actuating a valve needle connected to a valve-closure member. The valve-closure member cooperates with a valve seat surface to form a sealing seat. In this context, both an embodiment as a fuel injector opening to the outside as well as an embodiment as a fuel injector opening to the inside are possible. Although the piezoelectric actuator, assembled from a plurality of piezoelectric layers arranged in a stack, generates relatively strong lifting forces, it nevertheless generates relatively short valve travels. In the above-mentioned printed publication, it is therefore proposed to provide a hydraulic transmission device to increase the valve travel, between the valve needle and the piezoelectric actuator, transmitted to the valve needle.
One disadvantage in this known design is that, on the basis of the actuating elements, arranged serially one after the other, and made up of the piezoelectric actuator, the hydraulic transmission device having the transmission pistons, and the valve needle, the resulting design is relatively elongated. The known fuel injector therefore extends relatively far out of the cylinder head of an internal combustion engine, which is unfavorable for the assembly process, especially if the internal combustion engine is one that has four valves and only one camshaft.
In addition, it is disadvantageous that, for the transmission device, a special hydraulic fluid is used, which can escape due to leakage loss occurring over time. This can impair the mode of functioning of the transmission device and the service life of the fuel injector.
German Patent No. 43 06 073 describes a fuel injector having a piezoelectric actuator of a different design. In this fuel injector, a transformation of the motion of the piezoelectric actuator to the motion of the valve needle also occurs by way of a hydraulic transmission device. In the fuel injector known from this printed publication, the piezoelectric actuator, a lifting piston cooperating with the transmission device, and the valve needle are arranged serially one after the other, so that the resulting type of construction is relatively long. In addition, the potential leakage loss of the hydraulic fluid is disadvantageous here as well.
In contrast, the fuel injector according to the present invention has the advantage that, due to the bent, lateral arrangement of the actuator, the result is a smaller longitudinal extension in the fuel injector according to the present invention. In this context, the actuating direction of the actuator runs essentially perpendicular to the movement direction of the valve-closure member and of the valve needle. As a result of the lateral arrangement of the actuator, the fuel injector protrudes from the cylinder head less than in the case of the fuel injectors known from the related art, so that the installation space for the camshaft, intake and outlet valves, a spark plug, and other components of the internal combustion engine is not reduced. Especially in an internal combustion engine having four or more valves per combustion chamber and only one camshaft, there is, for the fuel injectors, only a limited installation space available, which is used in the design according to the present invention in a space-saving manner.
The change in the direction of motion of the actuator, which is actuated perpendicular to the direction of motion of the valve-closure member, is advantageously effected by a hydraulic transmission device. The hydraulic transmission device, in this context, fulfills a double function: first, it is used for transforming the lift, in order to transform the relatively small actuating lift of the actuator into a relatively large lift of the valve-closure member; second, it is used to change the direction of motion from the direction of motion of the actuator to the direction of motion of the valve needle and of the valve-closure member, which are perpendicular to the former.
It is advantageous in this context that the hydraulic transmission device is configured such that a transmission chamber filled with a hydraulic fluid is bent in an L-shape. In this context, a first transmission piston actuated by the actuator is connected to a first arm of the transmission chamber, and a second transmission piston acting on the valve needle is connected to a second arm of the transmission chamber. If the fuel injector is one that opens to the inside, the second arm of the transmission chamber is advantageously situated on the side of the second transmission piston facing the valve-closure member, in order to generate a lifting motion directed to the inside. Conversely, the second arm of the transmission chamber is situated advantageously on the side of the transmission piston facing the valve-closure member, if the fuel injector is one that opens to the outside.
The fuel supplied to the fuel injector and spray-discharged by the fuel injector is used as the hydraulic fluid for the transmission device. Therefore, no special hydraulic fluid, for example, a hydraulic oil, needs to be put into the fuel injector, which could escape due to leakage loss over time. Rather, a quasi-static fuel is continually replenished as the hydraulic fluid, automatically via guide apertures.
A biasing element advantageously surrounds the actuator in a sleeve-like manner. In comparison to a serial arrangement of the biasing element and the actuator, this increases the compactness of the fuel injector according to the present invention.
The valve needle is preferably composed of two valve needle segments, a first valve needle segment being designed as a single piece so as to include one of the transmission pistons, and the other valve needle segment is configured as a single piece so as to include the valve-closure member. The two valve needle segments can be connected by a coupling piece in a simple fashion. This makes assembly of the fuel injector according to the present invention significantly simpler.